As the demand for higher capacity transport aircraft increases, new and innovative fuselage designs accommodating increased capacity have caused the designers to reach into unconventional fuselage designs. One such design is a fuselage that has a double lobe cross section, wherein the cross section includes two conventional circular cross section fuselages that are laterally joined together. Although such a design permits a significant increase in either passenger or cargo capacity, or both, it is not without its problems.
A major problem associated with a fuselage having a double lobe cross section stems from the very geometry that gives it a significant advantage in capacity over fuselages having a circular cross section and the fact that the interior of the fuselage must be pressurized. Modem commercial aircraft often cruise at altitudes that exceed 30,000 feet above sea level. At these altitudes, as well as altitudes significantly lower, the oxygen content in the air is significantly less than that required to maintain the consciousness of the crew and passengers. Thus, either the passenger and crew compartments must be pressurized to simulate near sea level atmospheric conditions, or each and every person on board must be provided with an oxygen mask. Because the latter solution is not a reasonable or preferred alternative, the fuselage must be pressurized.
As is well-known in the art, vessels that are subjected to internal pressurization tend to naturally expand to a circular cross-sectional shape and, therefore, the optimum configuration for a pressurized vessel is circular. A pressurized vessel that is noncircular in cross section is subjected to significantly increased loads because of the tendency of the fuselage to expand to a circular cross section. In the case of a fuselage having a double lobe cross section, the unusually high loads occur at the crown and keel of the fuselage, that is, at the top and bottom of the fuselage where the two lobes are laterally joined together. The increased load at the crown and keel, if left unreacted, may cause the fuselage to pull apart at the crown and keel when the fuselage is pressurized. Thus, there exists a significant need for a structure stiffening assembly to prevent the fuselage from pulling apart.
In the past, the crown and/or keel beam structure, as well as the associated fuselage structure, would be stiffened or otherwise strengthened to react the increased loads. However, because of the unusually high loads associated with a double lobe fuselage, the amount of stiffening required to react these loads would result in an unreasonably heavy aircraft. Therefore, simply stiffening the keel and crown beams, as well as the associated fuselage structure, is not a reasonable option to react the loads associated with a fuselage having a double lobe cross section.
Utilizing a series of posts rigidly and permanently attached between the crown and keel beams to maintain the shape of the pressurized fuselage would obstruct the movement of cargo containers or pallets within the fuselage from one lobe into the other. Therefore, static posts disposed within the fuselage and spanning between the crown and keel of the fuselage are also an unsatisfactory solution to react the increased loads due to the double lobe shape of the fuselage.
Thus, there exists a need for a relatively simple and weight efficient assembly to react and transfer large loads resulting from the pressurization of the multiple lobes. The present invention addresses these and related issues to overcome the limitations currently encountered by fuselage strengthening mechanisms currently available in the art.